In EKG analyses of the heart condition of a patient and for various other bioelectrical purposes, it is important as a diagnostic tool and as a measure of these conditions during surgery or recovery of a patient, to tap bioelectrical signals from the human body and evaluate or plot these signals as a function of time.
In EKG measurements, for example, potential differences longitudinally of the cardiac muscle fibers are analyzed. In the recording of the EKG, the electrical potential is registered as a function of time over a succession of heart beat signals between spaced-apart locations on the surface of the body of the patient by electrodes in contact with the skin.
So that these potentials may be detected at the surface of the skin, the electrodes are usually adhered to the skin and, to eliminate the effect of a superficial skin resistance, an electrode gel is applied between the skin and the electrode.
This gel is a conductive material which causes problems. For example, upon removal of the electrode, residues of the gel are left on the skin and must be removed.
Furthermore, the electrodes are connected by cables with a heart-frequency meter and usually must be spaced as far apart as possible, generally between 6 to 14 cm, so that bipolar effects at the skin surface do not detrimentally affect the potentials which are to be monitored by the EKG.
It has also been proposed (see, for example, the German patent document--open application--Offenlegungsschrift--DE-OS No. 1,566,162) to create an unpolarizable condition at the electrode by inserting between the electrode material and the skin a porous paper disk permeated with silver chloride. This system has the disadvantage that such additional elements must be handled by the EKG machine operator or technician.
German Patent document No. 27 42 058 discloses a double electrode arrangement in which the electrode bodies are mounted on a common insulating support. In this arrangement the skin-contact resistance reduces the level of the bioelectric signal which is to be monitored and, as a result a conductive gel must be applied.
Furthermore the spacing between the electrodes must be relatively large if interference is to be avoided because of the conductive gel.